This invention relates to evaporative emission control systems of the type that are commonly used in association with internal combustion engines of automotive vehicles.
In such an evaporative emission control system, excess fuel vapors from the fuel tank are collected in a canister which must be periodically purged to the engine's induction system so that the vapors can pass into the engine's cylinders for combustion. In this way, the excess vapors do not escape to atmosphere where they may otherwise contribute to air pollution. The periodic purging of the vapor collection canister is conducted when conditions conducive to purging exist, and therefore it is a customary practice to have a canister purge solenoid (CPS) valve exercise control over the venting of the canister to the induction system and to place the CPS under the control of the engine electronic control unit (ECU). Because the ECU receives signals representing various engine operating parameters, it can be programmed to allow purging of the canister at different rates depending upon the prevailing engine operating conditions. Thus at certain times, greater amounts of purging may be permitted while at others, lesser amounts may be allowed.
Governmental regulations establish limits for the amount of fuel vapor that is permitted to be emitted from an automotive vehicle to atmosphere. The establishment of stricter regulations may impose heavier burdens on evaporative emission control systems such that the present systems may not be able to achieve compliance. Accordingly, there is a need for further improvement in the existing evaporative emission control systems of automotive vehicles so that increased flow rates of excess fuel vapors can be successfully handled. The present invention is directed to a solution for meeting this need.
The disclosed preferred embodiment of the present invention comprises the inclusion of a variable orifice in the vapor flow path from the canister to the induction system and the use of the engine's throttle to exercise control over the degree of restriction imposed by the variable orifice on the vapor flow path to the induction system. The variable orifice is progressively increasingly restricted as the engine is progressively increasingly throttled. A purge regulator that is under the control of the engine ECU also exercises control over the vapor flow to the induction system. The ECU is programmed using conventional programming techniques to produce a desired degree of purge flow regulation in accordance with engine operating conditions detected by the ECU. Thus, principles of the invention contemplate the conjoint control of the vapor flow from the canister to the induction system by the throttle's control of the variable orifice and by the ECU's control of the purge regulator.
A modern internal combustion engine that contains an ECU typically has a throttle position sensor that provides to the ECU an indication of the instantaneous throttle position. By having the variable orifice directly controlled by the throttle, the throttle position sensor signal is made inherently representative of the degree of restriction imposed by the variable orifice on vapor flow from the canister to the induction passage. Thus, the ECU can "read" the variable orifice and take that reading into account as it exercises control over the purge regulator.
The invention is well suited for providing controlled canister purging over a large dynamic range extending from engine idle to wide open throttle. It is also capable of providing a steadier flow that is beneficial in attenuating hydrocarbon emission spikes in the engine exhaust.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at this time in carrying out the invention.